An expandable medical implant for supporting bone structures includes a curved outer member to cooperatively engage a first bone structure and a curved inner member configured to cooperatively engage a second bone structure. The curved inner member is receivable within and movable relative to the curved outer member along an arc bounded by the curvature of the curved outer member. One of the curved outer and inner members may include a tapered surface and the other of the curved outer and inner members may include a scalloped surface. The implant may include a locking element disposed between the tapered and scalloped surface. The locking element is movable between a locked position engaging the tapered surface and a roughened locking surface to inhibit a decrease in the overall height of the implant and an unlocked position permitting at least an increase in the overall height of the implant.